Ganoderma lucidum is a mushroom with numerous medicinal properties. It is usually grown on substrates based on hardwood sawdust that is supplemented with costly additives, such as wheat or rice bran. It is well-established that substrate composition significantly affects the mycelial growth of G. lucidum. In our previous review study, we proposed that substances that stimulate extracellular enzyme secretion can replace expensive additives. Among such substances, inorganic compounds are cost-effective and are appropriate candidates. This study determined the effect of manganese, sodium nitrate, and ammonium nitrate on the mycelial growth of G. lucidum. Wheat straw was used as a growing substrate, and the supplements included manganese, sodium nitrate, ammonium nitrate, wheat bran or flour, and sucrose. These additives had concentration-dependent effects on mycelial growth. Higher concentrations of sucrose, sodium nitrate, and ammonium nitrate retarded mycelium growth significantly. Comparing the mycelium growth rate, manganese could replace wheat bran or flour as a more cost-effective additive.